Whereas significant improvements have been made in the development of drive trains for wind turbines, problems remain with regard to lifetime of mechanical drive elements, notably with regard to gearboxes. The lifetime of gearboxes is negatively influenced by torsional vibrations in particular.
Aerodynamic forces acting on the rotor blades of the wind turbine, and/or forces from interacting gearwheels in a gearbox of the drive train, such as so-called gear meshing frequency, may excite torsional resonances in the drive train. As a consequence of excited torsional resonances, undesired loads are imparted on the drive elements of the drive train. It has moreover been found that tonality, i.e. noise emitted from the wind turbine, occurs as a consequence of torsional vibrations in the drive train.
Prior art document WO 2007/140787 discloses a wind turbine comprising a detuner, which is employed to at least partially control the torsional resonance frequency of the drive train or components thereof. The detuner may e.g. comprise an adjustable damper as disclosed in European Patent Publication No. EP 1 197 678.
Though the wind turbine of WO 2007/140787 presents a clear progress in the reduction of tonality, it has been found that problems still exist in this regard, in particular, but not exclusively, in wind turbines comprising multi-stage gearboxes. Hence, one object of the invention is to provide an improvement to the drive train of a wind turbine that reduces the risk of excitement of torsional resonances in the drive train, and particularly in drive trains including multi-stage gearboxes.